The United States has the largest and fastest growing market for electronic cigarettes (e-cigs), and adult women of childbearing age are the most common users. However, no data exist regarding the health effects of e-cigs on pregnant women or their babies. It is well known that tobacco use during pregnancy is the most modifiable risk associated with adverse birth outcome, yet nearly one in four women in Kentucky continue to use tobacco products during pregnancy. E-cigs also contain varied (unregulated) concentrations of nicotine, despite nicotine being classified as a pregnancy class-D drug (exhibiting teratogenic effects on the fetus). The addictive nature of nicotine may explain continued use during this vulnerable time. E-cigs have been the center of recent controversy regarding novel smoking cessation or harm reduction products. There is also concern that marketing strategies promoting harm reduction may increase the appeal and obfuscate the known adverse effects of nicotine on fetal development. In addition to the adverse effects of prenatal nicotine, maternal tobacco use alters immune response during pregnancy, placing women at increased risk for preterm birth. We plan to build on previous work to determine the impact (better, same, or worse) that e-cigs and dual use (conventional + e-cig) have on prenatal immune response and birth outcomes compared to conventional use and dual use. Our overall goal is to determine the effects of e-cigs (and dual use) on perinatal biomarkers and birth outcomes. Three hundred and sixty pregnant women will be recruited. Participants will complete a survey to measure tobacco related behaviors, and provide perinatal biomarkers at four time points (each trimester and postpartum). Data analysis will include a series of repeated ANCOVAs to determine the association of perinatal cigarette smoking (conventional, e-cigarettes-only, and dual use) with perinatal biomarkers. A one- way ANCOVA will be used to determine the association with birth outcomes. Primary biomarker measures include: expired air carbon monoxide, urine and serum cotinine, serum immune markers and urinary NNAL. Gestational age at birth and birth weight are the primary birth outcomes. Until more data about the effects of e-cigs and dual use on perinatal immune response and birth outcomes are available, promotion of e-cigs during pregnancy would be premature. There is an urgent need to investigate the impact of e-cigs and dual use on perinatal biomarkers and birth outcomes. The lack of research may unnecessarily place women-and their babies -at risk for lifelong adverse health outcomes.